This invention relates to a single cylinder four stroke engine and more particularly to such an engine incorporating a turbocharger whose output is buffered by an air capacitor.
Turbocharging increases the power density of internal combustion (IC) engines, compared to naturally aspirated engines, by forcing more fresh air into the combustion chamber to burn more fuel. Most modern diesel engines, with the exception of single-cylinder engines, use turbocharging to generate more power from a smaller capacity, lighter engine than could be achieved through natural aspiration. Turbocharged engines are also more efficient than naturally aspirated engines of equivalent power, as frictional losses within an engine scale with its size. Conventional single-cylinder, four stroke IC engines are difficult to turbocharge because the intake and exhaust strokes are out of phase; when the turbocharger is powered by exhaust gasses, fresh air cannot be pumped into the engine because the intake valve is closed.
In some applications, it is practical to add additional cylinders to an engine so it can be turbocharged. This is a cost-effective solution for vehicles such as three-cylinder economy cars, as the engine cost is a relatively small fraction of the overall vehicle cost. But in smaller applications such as motorcycles, tractors, generators, and water pumps, engine cost is a large fraction of the overall device cost and there is an economic advantage to having a single cylinder, which has fewer precision-machined parts. Adding a turbocharger to a single-cylinder engine costs as little as 20% as much as adding an additional cylinder.